The use of a hydraulic piston to control the position of a synchronizer sleeve is well known. A representative system of that type is shown in U.S. Pat. No. 5,233,878, issued Aug. 10, 1993, in the name of Klemen et al. and assigned to the assignee of the present invention. These systems have a double acting piston which is pressurized to translate a shift fork to predetermined operating positions. The shift fork is operatively connected with a synchronizer which--in combination with fluid operated torque transfer friction devices, generally in the nature of clutches or brakes--establishes two distinct power paths in a countershaft transmission, such as that shown in U.S. Pat. No. 5,009,116, issued Apr. 23, 1991, in the name of Ordo et al. and assigned to the assignee of the present invention. In the aforesaid two patents, a hydraulically operated shift fork controls positioning of the forward-reverse synchronizer. When the synchronizer has been positioned, the power path in the transmission is completed by engaging the appropriate fluid operated torque transfer device.
Heretofore, a plurality of mechanical, hydraulic or electrical arrangements, as well as combinations thereof, have been devised to operate the several torque transfer devices used in power transmissions to sequence the drive ratios or "gears" provided by the transmission. The present invention is directed to a simplified arrangement that is particularly adapted to effect sequential operation of a twin countershaft automatic transmission that provides five drive ratios.